This is a big question with a lot of different answers. First, we need energy to power us just like any other machine and this comes from food that we eat and oxygen that we breathe. Then we need materials for growth and repairs, such as calcium for bones and iron for blood and protein for muscles. We have the capacity to grow from a single cell to a baby who weighs a few pounds to a very large adult who may weigh as much as 200 pounds or more. These materials for growth and repairs come from food also.
We need some way to move from place to place and to carry out tasks, so muscles attached to our skeleton allow us to do these things. In order to stay warm and cozy, our organs and muscles produce heat from their activity and this uses up some of the energy that we get from food. Our bodies need protection from diseases, and this protection comes from our built-in immune system. Sometimes our immune system is given a boost when we get a vaccination against a specific disease, such as for measles or polio or flu. There are several organs that carry out essential tasks. Two of them are the lungs and the heart. The lungs take in air that contains oxygen that all our tissues need. The heart pumps blood to the lungs to pick up oxygen and then distributes it, along with other substances, to the rest of the body. There are other organs, such as the liver, the kidney, various glands, and the stomach that carry out useful functions, but one of the most important organs is the brain. The brain controls many activities in the body including how we think and act.
With all of these complex parts that are continually working together, it is amazing that the human body doesn't break down more often than it does. When it does break down, we have medical doctors and nurses to help keep the human body operating smoothly. When we get very old, the parts of the body often don't work as well as they did when we were young and eventually it is impossible to keep the body alive. But humans live longer than almost all other animals.
Now, most mammals' bodies work about the same way as ours, because we are all distantly related. But there are some important differences between us and other animals. Some of the things that we humans can do that no other animals can is to appreciate music and play musical instruments, which requires manual dexterity and a lot of brain power, to think about and create complicated things, and to worry about our future and about our past, to laugh and cry, to walk and run on two feet, and to feel love and intense attachment to other people. These differences are pretty important and should make us proud to be human.